Bought these for the occasional wedding gig when I need to keep the volume down. They work as expected - the ability to move the rings up and down in order to change the sound is useful. Unfortunately, when playing, the rubber rings tend to move, which obviously changes the sound a bit. In the process of trying to keep moving them back, the rubber suffers. Despite only using these a handful of times, the rubber on one of mine has now started to split. I've ended up using tape wrapped around the rubber to keep it in place.
Overall they do what you want, but I would question the durability.
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